The present invention relates to a method of reducing the contamination level of a solvent purification system, and hence the volume of a waste stream. The invention also relates to such a solvent purification system.
A major problem with conventional cross-flow membrane units, such as cross-flow reverse osmosis, ultafilteration, and electrodialysis units, for example to remediate contaminated water or some other solvent, is the relatively large waste stream (for example approximately 40-60% of the total volume through the unit is a waste stream) that is generated and for which disposal is expensive.
A number of processes for treating solute-containing solvents are known. For example, U.S. Pat. No. 5,403,490, DESAI, discloses the use of a reverse osmosis unit, but cannot handle high solubility solutes and is suitable only for metals and some organic materials. The process of this patent also has a limited practicality because the process encourages fouling of the reverse osmosis unit. U.S. Pat. No. 5,158,681, Freedman et al, provides a reverse osmosis unit, but does not provide for treatment of the waste stream therefrom. U.S. Pat. No. 5,118,423, Astegger et al, again provides a reverse osmosis unit, but is not concerned with treating the waste stream therefrom. U.S. Pat. No. 5,238,574, Kawashima et al, discloses two reverse osmosis units and an evaporating device. U.S. Pat. No. 4,752,363, Buckley et al, discloses a cross-flow filtration process, along with the use of a filter. U.S. Pat. No. 4,284,492, Karn, provides a reverse osmosis electrodialysis system, and teaches how to prevent precipitation. U.S. Pat. No. 4,806,244, Guilhem, provides a sorption process to selectively remove ions from an aqueous stream. Finally, U.S. Pat. No. 4,244,506, Stokes, Jr. et al, discloses use of a cross-flow reverse osmosis unit in conjunction with a filter. None of these known devices successfully reduces the volume of a waste stream exiting a reverse osmosis unit.
It is therefore an object of the present invention to provide an improved method and system to reduce the contamination level of a solvent purification system and to thus reduce the volume of the waste stream from a cross-flow membrane unit.